In switching applications wherein two output devices are switched in response to the same input control signal, it is often desirable to switch one output device off before switching the other output device on. For example, in a motor direction control circuit, a current sourcing device and current sinking device for controlling the direction of current flow through a motor are alternately operated in response to an input logic signal. The logic state of the input signal controls which of the current sourcing or sinking devices is operated, and therefore represents the direction of motor rotation. In order to avoid sourcing and sinking current simultaneously, which would cause excessive currents when switching, the current sourcing device is turned off before the current sinking device is turned on and vice versa. The latter switching logic is commonly called "break before make" switching logic and is employed to avoid the condition wherein both output devices are simultaneously switched on, even momentarily.
Conversely, in other switching applications, the complement of "break before make", i.e., "make before break" switching logic is desirable in order to avoid the condition wherein two output devices are switched off simultaneously. Such condition is undesirable, for example, in switching first and second signal sources to an audio amplifier input wherein an open circuit condition at the amplifier input produces noise. In such case, it is desirable to connect the second signal source to the amplifier input before disconnecting the first signal source. In still further switching applications, it may be desirable to avoid a condition wherein one output device is on while the other is off.